The present invention pertains to processes and apparatus for the chemical conversion of solid polymers of tetrafluoroethylene and similar perfluoroolefins into useful fluorine-containing compounds of lower molecular weight by irradiation of the solid polymer with high-energy electrons in the presence of an inert or reactive gas.
The term perfluoroolefin as used herein is to be understood to include also perfluoroolefins in which one of the fluorine radicals has been replaced by a radical of another halogen such as chlorotrifluoroethylene.
It is known that, in order to depolymerize or react solid polymers of tetrafluoroethylene and similar perfluoroolefins with an inert or reactive gas in a zone that is irradiated with high-energy electrons, the solid polymers must be brought into intimate contact with the gas within the irradiation zone in the form of a powder. This is generally achieved by bringing the gases into contact with the surfaces of the particles of the powder or by passing the gases through a mass of the powder. In both cases, however, optimal contact between the gas and the solid particles cannot be achieved since, in the first place, the ratio of the surface area of the solid to its total volume is small and, in the second case, a so-called tunneling or formation of essentially unobstructed passages through the mass of powder generally occurs.
Irradiating particles of the solid polymer while it is suspended in the gas appears at first glance to be an ideal method of promoting such reactions. However, polytetrafluoroethylene when bombarded with or irradiated with high-energy electrons passes through several successive allotropic modifications or forms, namely, from a filamentous or feltlike form through a flourlike or powdery form, and finally to a viscous liquid form resembling honey, which thus also introduces other problems and difficulties that cannot be avoided in such processes.
Furthermore chemical reactions that are initiated and promoted by actinic or ionizing radiations, such as high-energy electrons, produce cleavage, substitution, and interchange reactions so that the resulting products are mixtures of compounds having widely differing compositions and molecular weights.
Polytetrafluoroethylenes can be decomposed or cleaved by heat or by the action of other forms of energy into oligomers of lower molecular weight and monomers. In attempts to obtain a complete conversion, however, the mass, as a rule, was completely decomposed, producing fluorine, cokelike substances, and various other fluorine-containing decomposition compounds.
Perfluoroolefins, especially perfluoroethylenes such as tetrafluoroethylene, can at present only be produced by conventional methods of synthesis. There is nevertheless an increasing demand for highly reactive compounds having high contents of fluorine and low molecular weight that are suitable for the production of perfluoroalkanoic and similar perfluorocarboxylic and perfluoroalkanesulfonic acids which are of great interest and importance for the production of textile auxiliaries, surfactants, biologically active substances and other valuable industrial chemical products. The fluorine-containing compounds are significantly superior with respect to their effects as well as their properties to related nonfluorinated compounds and they are further characterized by their great thermal and chemical stability, their incompatibility with water and oils, and their outstanding surface characteristics.